This research is based on the hypothesis that cell-surface molecules play critical roles in the differentiation and regulation of complex systems such as the nervous system. To explore this hypothesis, differentiation and tumor-specific antigens of the mouse nervous system will be recognized and defined using monoclonal antibodies from hybridomas. Cell populations defined by their antigenic differences will be purified and used in genetic, biochemical and biological studies of the component cells of the nervous system and of their surface molecules.